Different from a network technology in which communication is performed based on an internet protocol (IP) address or the like, as a network technology in which communication is performed based on the name of a content, information centric networking (ICN) has been and is being investigated and developed (for example, refer to Japanese Laid-open Patent Publication No. 2015-136098 and George Xylomenos et al., “A Survey of Information-Centric Networking Research,” COMMUNICATIONS SURVEYS AND TUTORIALS, VOL. 16, No. 2, 2014, pp. 1024-1049). As an investigation project for ICN, content centric networking (CCN) (for example, Japanese Laid-open Patent Publication No. 2009-277234), named data network (NDN) or the like is available.
For example, in the NDN, a request for content data from a client apparatus may be defined as “interest message.” In the interest message, a name of a content to be requested (hereinafter, abbreviated to “content name”) may be included. Each relay node in a network may relay an interest message to a server that provides the pertinent content in accordance with a forward information base (FIB) in which a relay destination corresponding to the content name is registered.
The server may generate a response defined as “data message” from content data corresponding to the content name in the interest message and transmit the response to the network. Each relay node in the network may relay the data message to the client apparatus along the route in the opposite direction to the relaying direction of the interest message.
The relay node may cache content data in the data message to be relayed into a database called content store (CS). If the content name in the interest message fully coincides with a content name of the data cached in the CS (hereinafter, abbreviated to “cache data”), the relay node may generate a data message including the cache data and transmit the data message to the client apparatus. Therefore, the relay node may not relay an interest message for requesting content data having a content name same as that of the cached data to the server.
In the NDN, a technology called keyword based content retrieval (KBCR) may be prescribed in which content data searched out from one or more servers is acquired based on a keyword. According to the KBCR, a search formula for a keyword is included into an interest message in place of the content name. This makes it possible to collect a plurality of content data that coincide with the keyword from a server or servers using a single interest message. Therefore, the convenience may be improved.
As described above, the relay node may transmit cache data to the client apparatus only when the content name in an interest message fully coincides with the content name of the cache data. Therefore, even if a large number of content data searched out using a keyword are cached in the CS in accordance with the KBCR, it may be difficult for the relay node to utilize the cache data unless the content names fully coincide with each other.
For example, it is assumed that a plurality of content data collected using a keyword “curry and rice” are cached in the CS. In this case, even if the relay node receives an interest message including a search formula of keywords “curry and rice” & (this signifies “and”) “potato,” since the content name is not included in the interest message, the relay node may fail to utilize the cache data relating to the keyword “curry and rice.”
Therefore, in the network, the interest message is relayed from the relay node to the server and a plurality of data messages corresponding to the interest message are relayed from the server to the client apparatus. Accordingly, the use rate of the transmission bandwidth may increase. Such a problem as just described may occur in a network system in which search for and acquisition of content data using a keyword are performed such as the KBCR. Taking the foregoing into consideration, it is desirable to be capable of reducing the use rate of the transmission bandwidth.